Same with me! But we have bigger problem - ZCO is trying to store signatures in "...\Signatures\*account_name*_files" folder. We have a localized versions of Office 2007/2010 (Polish language), so physically signatures are stored in "...\Sygnatury\" folder.
I've created this "\Signatures" folder and the error below is no longer appearing in my case, but because of the differences in the folder names I still cannot see signatures "downloaded" from Zimbra server in my Outlook.

<<
Same with me! But we have bigger problem - ZCO is trying to store signatures in "...\Signatures\*account_name*_files" folder.
>>
Are you sure?! Information associated with html signatures normally goes in "...\Signatures\*signature_name*_files" directory.

<<
We have a localized versions of Office 2007/2010 (Polish language), so physically signatures are stored in "...\Sygnatury\" folder.
>>
Ok - this is a completely separate issue from the above, right? I will raise a bug for this and get it fixed as soon as possible.